The invention relates to a data input module for inputting data by means of electrical contact for a monitoring/control installation.
Such a module is disclosed in Document EP-0101643. That module is designed primarily to detect a command input via an electrical contact and to supply necessary data to a monitoring/control installation. In Document EP-0101643, the electrical contact, e.g. a push button, is electrically connected to a detection member such as an optocoupler. That module is organized to incorporate only one electrical contact and only one detection member. Moreover, that known module does not include a test circuit for testing operation of the detection member.
Currently, standardizing manufacture of this type of data input module is desired so as to reduce its cost given that a module must be capable of including a plurality of contacts and a plurality of detection members, each detection member being associated with a contact and being installed on a support such as a printed circuit card. Furthermore, the potential difference across the feed inputs of such a module may vary to a large extent, e.g. in the range 48 volts to 127 volts, depending on the installation which receives the module. Therefore, in each individual case and as a function of the feed potential difference of the module, it is currently necessary to adapt the characteristics of the detection member contained in the module, and the number of contacts that can be implemented because of the problems due to the effects of heat dissipation from components on the support. Currently, when the potential difference to which the feed inputs of a module are subjected is 48 volts, 16 contacts can be implemented. When the potential difference is 127 volts, only 8 contacts can be implemented, in order to keep the dissipated power below a certain level.
In order to mitigate that drawback, a voltage regulator, e.g. a chopper voltage regulator, could be used having an output connected to the first terminal of the contact via the detection member, the output delivering a voltage that is lower than the optionally variable voltage applied to the first input of the module.
However, it is desired to use such a module with a plurality of contacts, each of which may require a minimum defined potential difference across its terminals for reliable operation, which potential difference is that across the inputs of the module. The minimum potential difference is such that, on contact closing, a self-cleaning spark is produced between the terminals of the contact. Otherwise, the terminals of the contact become oxidized over time, and the contact becomes isolating even when it is actuated.